Concrete is a preferred material for the construction of waste disposal systems, particularly lines and manholes. Concrete is relatively strong, inert and inexpensive, making it an ideal construction material. However, concrete is subject to corrosion from the acids, alkalis and salts, which are often present in the waste being removed, and particularly sulfide gases which are inevitably present. Sulfide attack can severely impair the operating life of unprotected concrete conduit systems.
It has been known for some time that the concrete of such waste disposal systems can be protected from sulfide attack by the provision of the suitable barrier between the waste fluids and the concrete. A number of plastic materials have been proposed for the protection of concrete under such operating conditions. For example, U.S. Pat. No. 4,670,315 discloses the application of a synthetic resin or plastic typically comprising a polyester, epoxide, polyurethane, acrylic, polyester or like resin to concrete. U.S. Pat. No. 4,578,235 discloses the use of polyvinyl chloride (PVC). U.S. Pat. No. 4,112,979 identifies in addition to modified or unmodified "rigid" PVC, polypropylene copolymers, polypropylene, acrylonitrile-butadiene-styrene, polycarbonate, polyacetal and polyethylene. Still other plastic lining materials are believed to have been used and suggested.
The protective plastic lining has been applied to the concrete body forming the pipe sections or manhole sections of such drainage systems in a variety of ways. U.S. Pat. No. 4,670,315 discloses the application of a synthetic resin or plastic directly to the concrete surface by spraying, rolling or troweling.
U.S. Pat. No. 4,578,235 discloses a process for manufacturing lined pipe in which a continuous flexible plastic sheet 107 is wound partially around a cylindrical mandrel to form a cartridge 22 which is thereafter inserted into a pipe-forming machine for the application of concrete around the cartridge to complete the formation of a lined concrete pipe. The liner disclosed in this patent extends only partially around the inner tubular or circumferential surface of the resulting pipe.
U.S. Pat. No. 3,562,056 discloses the on site construction of continuous, lined, concrete drainage pipe using an apparatus moved through a trench in which the pipe is located. The plastic lining in U.S. Pat. No. 3,562,056 is provided by individual formed plastic sections having connectors along their opposing edges. The linings are coupled together with their connectors extending circumferentially to provide a continuous, longitudinally extending lining. However, the lining extends over only an upper portion of the inner circumferential surface of the formed pipe which is exposed to the sulfide gases.
U.S. Pat. No. 2,816,323 discloses concrete pipes fully lined with plastic. A flexible length of plastic lining is rolled upon itself and two longitudinally extending, opposing edges overlapped to form a lap joint and provide a continuous inner circumferential surface. Lapped ends of the sheet are joined in a suitable manner such as by heat welding or the application of an adhesive or solvent.
U.S. Pat. No. 4,751,799 also discloses fully lining concrete pipe with plastic by the provision of a plurality of identical, vacuum-formed plastic sheet segments having adjoining longitudinally extending edges. The segments are joined together through separate mechanical joining members. Each lining also has a second pair of opposing edges which are turned generally perpendicularly to the remainder of the sheet to form annular exposed surfaces of the tubular ends of the resulting pipe. These end surfaces provide uniform, corrosion-resistant mating surfaces for end-to-end coupling of identical pipes. Butyl, silicone or other suitable caulking material is provided between the plastic end surfaces to provide a liquid-tight, corrosion-resistant seal in the joint.
U.S. Pat. No. 4,670,315 describes the process by which water vapor tends to diffuse from the soil through the concrete to the interface between the concrete and the plastic lining, creating an internal pressure which tends to separate the lining from the concrete. That patent suggests the use of a concrete bonding layer containing fibers projecting from the layer on which the plastic resins which are applied as the lining in that patent may anchor. U.S. Pat. Nos. 2,816,323, 4,578,235 and 4,751,799, for example, disclose the provision of preformed plastic linings having anchoring or engagement members which project outwardly from the linings and which flare outwardly in a direction generally parallel to the major adjoining surface of the plastic lining while projecting so as to be interferingly embedded in the concrete preventing pullout.